Arrangement for cleaning cutting fluid

ABSTRACT

The invention relates to a method and an arrangement for cleaning cutting fluid used for metal machining. The cutting fluid is withdrawn from the collecting tank (1) at a metal cutting machine by means of vacuum and conveyed to a central cleaning plant by way of a container (3) connected to a vacuum pump. From the cleaning plant the cutting fluid is returned to the collecting tank (1) at the metal cutting machine. The cleaning plant may with advantage comprise a separation tank (6), where separation takes place by gravity and a centrifugal separator (8).

TECHNICAL FIELD

The present invention relates to a method of cleaning cutting fluid usedfor the metal machining, at which the cleaning of the cutting fluidtakes place in a central cleaning plant and an arrangement for carryingthrough the method. The cleaning plant cleans the cutting fluid from anumber of collecting tanks.

In connection with metal machining cutting fluids have been used sincelong for lubricating and cooling. The cutting fluid shall cool the toolused for the cutting, the workpiece and the formed chips and reduce thefriction by forming a lubricating film between the sliding surfaces.Usually the cutting fluid contains among all corrosion protectingagents, emulsifiers and bactericides. Every metal cutting machine has ina collecting tank a supply of cutting fluid and from the tank thecutting fluid is pumped to a nozzle and sprayed over the workpiece andthe tool. When the cutting fluid passes the cutting spot it brings alonglarger and smaller metal chips. The larger metal chips are separated bypassing the fluid through some kind of straining means, for example aplate or a case provided with small openings, on its way to thecollecting tank. The cutting fluid is in addition to the metal chipsoften contaminated by oil, which spreads as a surface layer over thecutting fluid. In spite of the bactericides a growth of bacteria maytake place under the film of oil, which results in very ill-smellingbreaking down products. The staff handling the metal cutting machinesrun the risk of infections on arms and hands as a consequence of thefact that the cutting fluid is contaminated with bacteria, solidparticles and oil.

BACKGROUND ART

Earlier contaminated cutting fluid has been cleaned centrally byconveying the cutting fluid through pipelines in and below the floor toa cleaning plant in connection with a central tank. Contaminants ofmetal have been separated by passing the cutting fluid through differenttypes of filter. Oil has been removed from the surface of the tank bymeans of a bandskimmer. It is very difficult to remove all of the oilwithout bringing along a large part of cutting fluid, which makes themethod uneconomical.

According to the invention a method and an arrangement for cleaning ofcutting fluid is now proposed which may easily be installed in existingengineering plants without any expensive changes or rebuildings andwhich implies that important advantages are achieved for the staff atthe metal cutting machines, which no longer have to be exposed toill-smelling gases and skin irritation by metal chips and oil in thecutting fluid.

DISCLOSURE OF INVENTION

The method according to the invention is characterized mainly in thatcontaminated cutting fluid by means of vacuum is conveyed from thecollecting tank at the cutting place to a container, which is connectedto a vacuum pump. From the container the contaminated oil is conveyed toa cleaning plant and is thereafter returned to the collecting tank. Bysucking the cutting fluid in this way from the collecting tank to thecleaning plant it is possible to avoid bulky transporting arrangementsin and below the floor or an expensive manual handling and also to avoidthe use of pumps which may be damaged by the small metal particles whichfollow the cutting fluid. A cleaning system according to the inventionis also very flexible. It may easily be adapted to the location of thecutting machines in the plant and further cutting machines may easily beconnected to the cleaning plant. The cleaning of the cutting fluid maytake place continuously when the metal cutting machine is working. It isalso possible to suck the cutting fluid to the cleaning plant at shorteror longer intervals.

According to the method of the invention the main part of the cuttingfluid is brought to circulate in order to cool and lubricate the tooland the workpiece, while a lesser part of the content in the collectingtank is sucked away and conveyed to the cleaning plant. This indicatesthat if some error should occur in the cleaning plant there is anyhowenough fluid to make metal cutting possible.

In order to convey the cutting fluid back to the cutting place thecleaned cutting fluid is put under pressure, when the cutting fluid haspassed the cleaning plant.

The contaminated cutting fluid is according to the invention withadvantage cleaned by passage through a separation tank. In thisseparation tank a separation by means of gravity takes place since lightcontaminants, as oil, collected in the upper part of the separation tankwhereas metal chips and heavy contaminants sink to the bottom of theseparation tank. From the separation tank a first fraction containingcutting fluid and light contaminants is withdrawn and this fraction isled to a separator, for example a centrifugal separator. The cleanedcutting fluid withdrawn from the separator is together with a secondfraction from the separation tank mainly containing cutting fluidconveyed to a second tank in which the collected cutting fluid is putunder pressure and returned to the collecting tank at the cutting place.Owing to this combination of cleaning steps an efficient cleaning of thecontaminated fluid is obtained with relatively simple means as well asan essential reduction of the amount of bacteria, solid particles andoil in the cutting field.

According to the invention an arrangement for carrying through thedescribed method of cleaning cutting fluid is also suggested. Thisarrangement mainly comprises a pipeline arranged to be placed undervacuum, which pipeline at one end opens under the surface in acollecting tank for cutting fluid and in its other end is connected to acontainer, which in its turn is connected to the vacuum pump. Thearrangement also comprises a cleaning plant for contaminated cuttingfluid which has been sucked away from the collecting tank and a secondpipeline by the aid of which cutting fluid is returned to the collectingtank.

The proposed arrangement is further preferably provided with a secondtank for cleaned cutting fluid, which is connected between the cleaningplant and the second pipeline, which second tank is provided with meansin order to put the cutting fluid under pressure.

The cleaning plant according to the invention suitably comprises aseparation tank with a tangential inlet for contaminated cutting fluidand a first outlet for a first fraction comprising cutting fluid andlight contaminants and a second outlet for a second fraction consistingmainly of cutting fluid. The first fraction is led to a separator, forexample a centrifugal separator, and from this a heavy phase containingcleaned cutting fluid and a light phase containing light contaminantsare withdrawn. The outlet for heavy phase from the separator and thesecond outlet of the separation tank are connected to the second tankmentioned above.

The separation tank is with advantage designed such that in its centrethere is arranged an insertion with walls which inside the insertiondefine two fluid chambers delimited from the fluid chamber in theseparation tank. The first of these fluid chambers has an inlet whichconsists of a brim inlet from the fluid chamber in the separation tankand an outlet which extends through the fluid chamber in the separationtank. The second fluid chamber has an inlet which is connected to thefluid chamber in the separation tank in such a manner that the sameliquid level is obtained both in the separation tank and in the secondfluid chamber and an outlet which extends out of the separation tank. Alevel-holding means is arranged to sense the liquid level of the secondfluid chamber and supply clean fluid when the level sinks.

BRIEF DESCRIPTION OF DRAWINGS

The proposed method of cleaning cutting fluid and an arrangement forcarrying through this method are described closer with reference to theenclosed drawing,

FIG. 1 of which shows a flow chart of a preferred embodiment of theinvention and

FIG. 2 of which schematically shows an embodiment of a separation tankused for the described embodiment. In the flow chart obvious detailslike valves have been omitted.

BEST MODE OF CARRYING OUT THE INVENTION

In FIG. 1 a number of collecting tanks for cutting fluid at cuttingmachines are shown. From the collecting tanks 1 contaminated cuttingfluid is conveyed to a container 3, by way of a pipeline 2. The pipeline2 may with advantage be arranged at some height over the metal cuttingmachines, in the same way as in a pipeline milking plant. The container3 is connected to a vacuum pump 4 and by means of this the container 3and the pipeline 2 are put under vacuum. At each connection the pipeline2 ends just below the surface in the collecting tank. The cutting fluidcontaminated with oil is sucked on to the cleaning plant, while theheavier metal particles remain on the bottom of the collecting tank.From the container 3 the contaminated cutting fluid is conveyed to theseparation tank 6 by way of a pipeline 5. The inlet for cutting fluid isarranged such that the cutting fluid is given a tangential movement inthe separation tank. Light contaminants are at this gathered near thesurface in the middle of the separation tank and from there a fractionis withdrawn which is directed to a separator 8 by way of a pipeline 7.The mixture of cutting fluid, sludge and metal particles, which areseparated in the separation tank 6, is conveyed to pipeline 7 by way ofpipeline 7a.

In the shown embodiment of the invention the separator consists of acentrifugal separator but it is also possible to separate lightcontaminants from the cutting fluid by means of a skimmer, while heavycontaminants are separated by means of filter.

Through the light phase outlet 9 of the centrifugal separator oil andother light contaminants are withdrawn and through the sludge outlet 9asolid contaminats. The obtained heavy phase which contains cleanedcutting fluid is conveyed to a second tank 11 for cleaned cutting fluidby way of a pipeline 10. A second fraction from the separation tankwhich mainly contains cleaned cutting fluid is also transported to thetank 11 by way of a pipeline 12. The cutting fluid is put under pressureby means which not are shown and returned by way of the pipeline 13 tothe collecting tanks 1 at the cutting machine. Also pipeline 13 may bearranged over the machines. The collecting tanks are with advantageprovided with liquid level indicators (not shown in the drawing) inorder to hinder that the tanks overflow. There is also a throttling atthe inlet of pipeline 2 in order to control the amount of air suckedinto the vacuum system (not shown in the drawing).

In FIG. 2 there is shown the separation tank 6 with a tangential inlet14 connected with the pipeline 5. In the separation tank 6 there is alsoarranged an insertion with two coaxial, cylindrical walls 15, 16 and abottom 17. In the insertion these walls separate two fluid chambers 18,19 delimited from the fluid chamber in the separation tank. In thisembodiment the insertion consists of two coaxial cylinders but it may ofcourse be designed in some other way as long as the in- and outlets ofthe insertion are designed such that the same flow conditions that aredescribed below are obtained. The upper edge 20 of the cylindrical wall15 is arranged such that the edge is situated just below the liquidlevel in the separation tank. The inlet to the fluid chamber 18consequently consists of an annular brim inlet over the edge 20. Thefluid chamber 18 also has an outlet 21, which extends through theseparation chamber and is connected to the pipeline 7. Inside the wall16 there is a second fluid chamber 19. In this second fluid chamber 19there is arranged a pipe 22, the lower part of which is fastened to thebottom of the insertion and the upper end of which is situated at thesame level as the edge 20. Through this pipe the fluid chamber 19 isconnected to the fluid chamber in the separation tank. In the bottom 17of the insertion there is also arranged an outlet 23 from the fluidchamber 19 which is connected to the pipeline 12. A level sensing means(not shown in the drawing), for example a float, is also arranged in thefluid chamber 19, which means actuate a valve 24 in a feed pipe 25 forclean cutting fluid. In the bottom of the separation tank there is alsoan outlet pipeline 26 for sludge separated in the separation tank, whichpipeline is connected to the pipeline 7a.

The separation tank according to the invention is intended to work inthe following way. When the contaminated cutting fluid is conveyedtangentially into the separation tank light contaminants are gathered inthe middle of the tank and flow over the brim inlet into the fluidchamber 18. Heavy contaminants on the other hand sink towards the bottomof the tank and are collected there. Owing to the fact that the inlet tothe fluid chamber 19 is arranged on a certain depth in the separationtank the cutting fluid that is collected in the fluid chamber 19 will berelatively clean.

According to the invention the cleaning of the cutting fluid takes placein no less than four steps. The first step consists of the preliminaryseparation of heavier metal contaminants in the collecting tank, whilean upper fraction of the collecting tank is sucked to the cleaningplant. Step two consists of the passage of the container 3 in which acertain part of the heavy particles are gathered at the bottom of thecontainer, which particles intermittently are withdrawn from the bottom.Step three consists of the cleaning in the separation tank which isdescribed above. Step four consists of the cleaning in the centrifugalseparator from which, apart from the two liquid phases, a sludge phaseconsisting of small metal particles is withdrawn continuously orintermittently, which metal particles have not been separated in earlierseparation steps.

According to the invention a reduction of the amount of bacteria isobtained. This effect has also been shown experimentally, sincemeasurements have shown that the amount of bacteria, when cleaningaccording to the invention, has diminished from 10⁹ bacteria/ml to 10⁶bacteria/ml, which is considered as a satisfactory value. That theamount of bacteria has diminished is supposed to depend on the fact thataround the metal particles there is a thin film of oil, in which agrowth of bacteria takes place. When the small metal particles areseparated a certain amount of bacteria accordingly follow them.

I claim:
 1. The combination of a series of collecting tanks forrespective metal cutting machines, a cutting liquid in each said tankfor use in metal machining, a first pipeline having inlet branchesopening into said tanks in position to remove therefrom only an upperlayer of cutting liquid, a container into which the outlet end of saidpipeline leads, a vacuum pump connected to said container for creating avacuum therein to draw cutting liquid from said tanks into saidcontainer, means connected to said container for receiving cuttingliquid therefrom and cleaning said liquid, and a second pipeline forreturning cutting liquid from said cleaning means to said collectingtanks.
 2. The combination of claim 1, comprising also a additional tankinterposed between said cleaning means and said additional pipeline, andmeans associated with said second tank for maintaining the liquidtherein under pressure.
 3. The combination of claim 1, in which saidcleaning means comprises a separation tank having a tangential inlet forreceiving contaminated cutting liquid from said container, theseparation tank also having a first outlet for a first separatedfraction comprising cutting liquid and light contaminants and a secondoutlet for a second fraction consisting mainly of cutting liquid, aseparator connected to said first outlet for receiving said firstfraction from the separation tank, said separator having an outlet for aheavy phase consisting of cleaned cutting liquid, said separator alsohaving outlet means for separately discharging a light phase consistingof light contaminants, and ducts through which said second outlet ofsaid separation tank and said heavy phase outlet of said separator leadto said second pipeline.
 4. The combination of claim 3, in which saidseparator is a centrifugal separator.
 5. The combination of claim 3, inwhich said separation tank includes a main liquid chamber and first andsecond sub-chambers separated from said main chamber and substantiallysurrounded thereby, said first sub-chamber having a brim forming aliquid inlet from said main chamber and also having an outlet extendingthrough the separation tank, said second sub-chamber having an inletconnected to said main chamber and operable to provide the same liquidlevel in both said main chamber and said second sub-chamber, the secondsub-chamber also having an outlet extending through the separation tank,and level-maintaining means for sensing the liquid level in said secondsub-chamber and supplying fresh cutting liquid thereto when said sensedliquid level sinks.
 6. The combination of claim 1, in which saidcleaning means comprises a separation tank and a separator, saidseparation tank having a tangential inlet for receiving contaminatedcutting liquid from said container, the separation tank including a mainliquid chamber into which said tangential inlet opens, the separationtank also including first and second sub-chambers separated from saidmain chamber and substantially surrounded thereby, said firstsub-chamber having a brim forming a liquid inlet from said main chamberand also having an outlet extending through the separation tank andleading to said separator, said second sub-chamber having an inletconnected to said main chamber and operable to provide the same liquidlevel in both said main chamber and said second sub-chamber, the secondsub-chamber also having an outlet extending through the separation tankand leading to said second pipeline independently of said separator,said separation having outlet means for separately discharging a lightphase containing light contaminants, said separator also having anoutlet for a heavy phase constituting cleaned cutting liquid, said heavyphase outlet leading to said second pipeline.
 7. The combination ofclaim 6, in which said main chamber of the separation tank has a sludgeoutlet leading to said separator.